My invention relates to switching systems and to a centralized subsystem for use in switching offices for inproving the operation of office functions, such as dial tone return, digit reception and pretranslation. More particularly, my invention relates to a buffer circuit in the foregoing subsystem and which is effective for obtaining access for the subsystem to conventional office circuits and preferentially over other conventional office circuits which are competing with the subsystem.
In order to provide high quality service at low cost it is necessary that switching facilities, requiring large investments of time and money, be utilized for many years before they are replaced with improved facilities. Because of the long life of these facilities and the rapid technological advances in the art, it is desirable periodically to upgrade existing systems with improvements that can reasonably be retrofitted therein.
Once example of the foregoing occurs in switching offices, such as described in U.S. Pat. No. 2,585,904 of Feb. 19, 1952 to A. J. Busch, in which certain initial call functions, such as dial tone return, digit reception and control functions associated therewith, are standardly performed by individual originating registers. Although these registers operate satisfactorily, each one is required to complete certain control functions which could more advantageously be performed by a centralized control arrangement, thereby circumventing the necessity of providing redundant and expensive control circuitry in those originating registers added for growth purposes.
This specification discloses, by way of example, a computerized subsystem for performing the functions of originating registers and with improved operation. The subsystem comprises a plurality of pulse receivers, each having only minimum operative functions, and being controlled by a computer where all subsystem control functions reside. One of the functions performed by originating registers and now consolidated in the computer includes the determination on each arriving call as to whether a pretranslation is required of the initially received called party digits in order to determine the total number of such digits the office should expect. In conventional practice, each originating register interfaces with a conventional office connector through which access is gained to a pretranslator for obtaining the pretranslated information. The subsystem interfaces with the same connector for gaining access to the pretranslator. In serving a call, each office register competes with other registers for connector access on an equal basis. The subsystem, on the other hand, operates for simultaneously serving a plurality of calls and must therefore be afforded preferential connector treatment over the registers in order to obtain its equitable share of pretranslator services.
To elaborate, the connector, with which the register and subsystem communicate, comprises three independent subgroups. For providing for balanced traffic loading and increased reliability, the registers are assigned in approximately equal numbers to each subgroup with each register dedicated to only one subgroup. In this system arrangement, known techniques of achieving connector preference for the subsystem have proven to be inadequate. For example, subsystem preference could be achieved by assigning all registers to two of the three connector subgroups, thus reserving the third subgroup exclusively for serving the subsystem. Such an arrangement, however, injures the office traffic balance through the connector. Moreover, this arrangement decreases reliability in that a single failure of the third connector subgroup destroys the ability of the subsystem to obtain any of its pretranslation needs. Other preference arrangements are deemed unsatisfactory because of the foregoing traffic balancing and reliability criteria and because those arrangements undesirably require extensive modification of existing office equipment. I solve the foregoing problems by providing a novel buffer circuit for interfacing the control computer of the subsystem with the pretranslator connector so as to provide preferential access for the subsystem and, importantly, without sacrificing reliability or traffic balancing and without requiring any modification of the connector or other existing office circuits.